1. Field of the Invention
This invention relates to an improvement of the device for preventing the bounce or rebounding of the movable mirror of a single lens reflex camera.
2. Description of the Prior Art
As is well known, a single lens reflex camera has a movable mirror in front of the film surface. The movable mirror is obliquely disposed to form a predetermined angle, for example, 45.degree. relative to a phototaking optical path, and, when a release button is depressed, the mirror is retracted or pivoted upwardly out of the optical path to expose the film to a phototaking light through a focal-plane shutter. The retracted mirror abuts a stopper provided at an upper position in the camera and is held there during a predetermined exposure time to completely open the phototaking optical path. However, when the mirror is retracted it will be sprung back to produce a bounce whereby a part of the phototaking light path will be temporarily interrupted.
For preventing the bounce of the mirror, it has been proposed to weakening the retracting force or to locate the uppermost position of the retracted mirror extremely outside of the phototaking light path to decrease the effect of the bounce of the mirror. Further, there has been a proposal to use an air-damper as disclosed for example in U.S. Pat. No. 4,192,598 or to arrange a bounce preventing member having a cam surface to engage with a mirror driving pin as described in Japanese laid-opened utility model application No. 169522/1980.
However, when the retracting is weakened, the movement of the mirror becomes unstable, and when the uppermost position of the retracted mirror is set to a high position, it requires the camera body to be bulky. Moreover, when the air-damper is used, it is effective but costly. When the bounce preventing member having a cam surface to engage with the mirror driving pin is used, it was usual, for the purpose of decreasing the number of the constituting elements to decrease the cost, to move the bounce preventing member always following the movement of the mirror driving pin, and in this case the bounce preventing member must have a force opposing the movable mirror so that the actuation of the movable mirror becomes unstable similar to the case in which the retracting force to jump up the mirror is weakened. Further, if the cam surface to prevent descent of the mirror due to the bounce is shaped to operate more effectively, the cam surface will be too effective so that sometimes the movable mirror can not descend at all or the movement of the mirror becomes difficult at the time the movable mirror must come down after the shutter has been opened for a predetermined exposure time and the trailing curtain of the shutter was closed. Therefore, in practice, the cam surface must be used in a less effective shape.